I thought it took a few hours to fluff up. I once had to assist a chick out of their egg. And it didn’t fluff up for a few hours.
So here’s the assist story. A hen was broody. Started to throw eggs off it’s hidden nest up above in shelves in my storage trailer. My husband heard chirping and looked everywhere and didn’t find a chick. He saw an egg on the floor a bit cracked and just tossed it outside thinking it was a dud. We went back later and it was starting to get covered in ants. It was a live chick! We had to crack the egg and get all the ants out. It survived. Unfortunately the heat got it along with 4 of its siblings a week later (but before then it was strong and healthy). So sad, because I was the first anything it saw and thought we had a bond.